fix(prefixIds): does not handle SMIL timing offsets

[yangxu52]

This PR improves handling of begin and end attributes in the prefixIds plugin.

Problem

The current implementation only prefixes values ending with .end or .start, but valid SMIL syntax also includes offsets such as:

• a.end-0.5s
• b.begin+0.1s

These cases are currently ignored, leading to broken animation references after ID prefixing.

Solution

Replace the suffix check with a regex that correctly parses:
<id>.(begin|end)(+/-offset)?
This ensures all valid SMIL timing references are properly prefixed.

Impact

• Fixes broken animation chaining
• Maintains backward compatibility
• No effect on non-SMIL attributes

Example

Before:

begin="a.end-0.5s"

After

begin="prefix-a.end-0.5s"

Test

1. without offsets, like x.end, OK
2. with offsets, like b.end-0.5s, OK
3. mix and multiple, like x.begin;x.end-0.5s, OK

Test code e.g:

it('should prefix SMIL begin/end with offsets', () => {
  const svg = `
    <svg>
      <animate id="a" begin="b.end-0.5s" />
      <animate id="b" begin="a.begin+0.1s" />
    </svg>
  `

  const result = optimize(svg, {
    plugins: [
      'cleanupIds',
      {
        name: 'prefixIds',
        params: { prefix: 'p' },
      },
    ],
  })
  expect(result.data).toContain('p-b.end-0.5s')
  expect(result.data).toContain('p-a.begin+0.1s')
})

Notice
This PR intentionally keeps a minimal regex-based approach consistent with existing implementation, while extending coverage to valid SMIL offset syntax instead of all.

Linked Issue
Fixes: #2207 #2073